Battery charging starts and stops repeatedly when battery below 20%?

My 1020 battery is working well - no problems. But, I notice that when charging the battery from below 20% charge the charge process stops and starts repeatedly. I can hear the phone beep every time the charging process restarts. However, this does not seem to prevent the battery from achieving full charge within a few hours. It does not do this when charging the battery when the battery is not low.
- Anyone else noticed this?
- Could this be some kind of battery charge management to prevent overheating during the charging process?